244 SCIENCE AND METHOD. 



strainer, since the unoccupied spaces are much larger 

 than the occupied. To reaHze this, we must remem- 

 ber that Laplace demonstrated that the attraction, in 

 passing through the Earth, suffers a loss, at the very 

 most, of a ten-millionth part, and his demonstration is 

 perfectly satisfactory. Indeed, if the attraction were 

 absorbed by the bodies it passes through, it would no 

 longer be proportional to their masses ; it would be 

 relatively weaker for large than for small bodies, since 

 it would have a greater thickness to traverse. The 

 attraction of the Sun for the Earth would therefore be 

 relatively weaker than that of the Sun for the Moon, 

 and a very appreciable inequality in the Moon's motion 

 would result. We must therefore conclude, if we adopt 

 Lesage's theory, that the total surface of the spherical 

 molecules of which the Earth is composed is, at the 

 most, the ten-millionth part of the total surface of the 

 Earth. 



Darwin proved that Lesage's theory can only lead 

 exactly to Newton's law if we assume the corpuscles 

 to be totally devoid of elasticity. The attraction 

 exercised by the Earth upon a mass i at a distance i 

 will then be proportional both to S, the total surface 

 of the spherical molecules of which it is composed, to 

 V, the velocity of the corpuscles, and to the square 

 root of p, the density of the medium formed by the 

 corpuscles. The heat produced will be proportional 

 to S, to the density p, and to the cube of the 

 velocity v. 



But we must take account of the resistance ex- 

 perienced by a body moving in such a medium. It 

 cannot move, in fact, without advancing towards certain 

 collisions, and on the other hand retreating before 



